linux-kernel - Re: [PATCH] RISC-V/bpf: Enable bpf_probe

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Message-ID: <YsJOVZU1gPo3KzdB@ofant>
Date:   Mon, 4 Jul 2022 10:20:05 +0800
From:   Yixun Lan <dlan@...too.org>
To:     Conor Dooley <mail@...chuod.ie>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()

Hi Conor Dooley:

On 14:12 Sun 03 Jul     , Conor Dooley wrote:
> On 03/07/2022 14:09, Yixun Lan wrote:
> > Enable this option to fix a bcc error in RISC-V platform
> > 
> > And, the error shows as follows:
> > 
> > ~ # runqlen
> > WARNING: This target JIT is not designed for the host you are running. \
> > If bad things happen, please choose a different -march switch.
> > bpf: Failed to load program: Invalid argument
> > 0: R1=ctx(off=0,imm=0) R10=fp0
> > 0: (85) call bpf_get_current_task#35          ; R0_w=scalar()
> > 1: (b7) r6 = 0                        ; R6_w=0
> > 2: (7b) *(u64 *)(r10 -8) = r6         ; R6_w=P0 R10=fp0 fp-8_w=00000000
> > 3: (07) r0 += 312                     ; R0_w=scalar()
> > 4: (bf) r1 = r10                      ; R1_w=fp0 R10=fp0
> > 5: (07) r1 += -8                      ; R1_w=fp-8
> > 6: (b7) r2 = 8                        ; R2_w=8
> > 7: (bf) r3 = r0                       ; R0_w=scalar(id=1) R3_w=scalar(id=1)
> > 8: (85) call bpf_probe_read#4
> > unknown func bpf_probe_read#4
> > processed 9 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
> > 
> > Traceback (most recent call last):
> >   File "/usr/lib/python-exec/python3.9/runqlen", line 187, in <module>
> >     b.attach_perf_event(ev_type=PerfType.SOFTWARE,
> >   File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 1228, in attach_perf_event
> >     fn = self.load_func(fn_name, BPF.PERF_EVENT)
> >   File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 522, in load_func
> >     raise Exception("Failed to load BPF program %s: %s" %
> > Exception: Failed to load BPF program b'do_perf_event': Invalid argument
> > 
> > Signed-off-by: Yixun Lan <dlan@...too.org>
> 
> Do you know what commit this fixes?
> Thanks,
> Conor.
> 

I think this is effectively broken for RISC-V 64 at the commit:
 0ebeea8ca8a4: bpf: Restrict bpf_probe_read{, str}() only to archs where they work

However, the bcc tools haven't got BPF support for RISC-V at that time,
so no one noticed it

I can add a Fixes tag if you think it's a proper way

> > ---
> >  arch/riscv/Kconfig | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 32ffef9f6e5b4..da0016f1be6ce 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -25,6 +25,7 @@ config RISCV
> >  	select ARCH_HAS_GIGANTIC_PAGE
> >  	select ARCH_HAS_KCOV
> >  	select ARCH_HAS_MMIOWB
> > +	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> >  	select ARCH_HAS_PTE_SPECIAL
> >  	select ARCH_HAS_SET_DIRECT_MAP if MMU
> >  	select ARCH_HAS_SET_MEMORY if MMU

-- 
Yixun Lan (dlan)
Gentoo Linux Developer
GPG Key ID AABEFD55